A Worldwide Interoperability for Microwave Access (WIMAX) system, also called an 802.16 wireless Metropolitan Area Network (MAN), can cover a range of 25-30 miles in the data communication field.
The WIMAX technology is based on the wideband radio standards in the IEEE 802.16 series. Up to now, the IEEE 802.16 series include the IEEE802.16, IEEE802.16a, IEEE802.16c, IEEE802.16d, IEEE802.16e, IEEE802.16f, and IEEE802.16g standards. IEEE802.16, IEEE802.16a, and IEEE802.16d are fixed radio access air interface standards. IEEE802.16e is a mobile wideband radio access air interface standard. WIMAX adopts IEEE802.16e as its air interface standard.
IEEE802.16e is backward compatible with IEEE 802.16d. The physical layer implementation mode of IEEE 802.16e is similar to that of IEEE 802.16d. The main difference is that IEEE802.16e has extended Orthogonal Frequency Division Multiple Access (OFDMA) to meet the requirements for various carrier bandwidths. 802.16e has introduced many new features at the Media Access Control (MAC) layer to support mobility. The development trend of radio access technologies is to realize high capacity, wide coverage range, and mobility of the wideband radio systems by introducing new technologies, such as Orthogonal Frequency Division Multiplex (OFDM) and Multiple Input Multiple Output (MIMO) so that radio access technologies and 3G networks coexist and supplement each other. Therefore, IEEE 802.16e becomes a focus in the industry from its birth.
Based on IEEE 802.16e, WIMAX brings forward a new enhanced technology IEEE 802.16m. Currently, IEEE 802.16m has the following requirements: IEEE 802.16m can be used by mobile objects at the rate of over 350000 m/h; the maximum downlink data transmission rate is over 350 Mbps; the uplink data transmission rate is not smaller than 200 Mbps; the bandwidth is 5 MHz, 10 MHz, 20 MHz, and 40 MHz; a maximum of 4×4 MIMO may be used as planned. When a 20 MHz bandwidth and Time Division Duplex (TDD) are used for communications, the downlink and uplink area-based data transmission rates are 40 Mbps and over 12 Mbps respectively. In addition, the access time and handover delay of the data link layer are shorter than 10 ms and shorter than 20 ms respectively. IEEE 802.16m also needs to be compatible with IEEE 802.16e.
A WIMAX system includes Basic Stations (BSs) and Mobile Stations (MSs), which communicate through the electromagnetic waves transmitted and received by a wireless transceiver in wireless mode. Each BS is represented by a Basic Station Identity (BS ID) that is different from the BS IDs of other BSs, A BS ID is a 48-bit field. Each BS has its coverage range. A BS can communicate with the BSs in its coverage range. Each BS sends an MOB_NBR_ADV message to the BSs and MSs within a certain area regularly and saves the MOB_NBR_ADV message. The MSs receive and save the MOB_NBR_ADV message. The MOB_NBR_ADV message contains the BS IDs of the BSs in the area. The BS IDs are arranged in the MOB_NBR_ADV message in sequence. At the same time, one BS can communicate with multiple MSs in its coverage range, but one MS can communicate with only one BS at the same time, and this BS is called the serving BS of the MS. With the movement of an MS, the MS may pass through the coverage range of multiple BSs. In this case, the serving BS of the MS changes. The MS takes a BS that meets communication quality requirements as the serving BS to continue the communication, and this process is known as handover. To ensure communication continuity and reduce communication interruptions that may be caused by handover, an MS detects the signal quality of adjacent BSs continuously to determine a target BS for handover when the MS communicates with the current serving BS normally. This continuous detection process is called scanning. Thus, the MS can be handed over to a BS with better communication quality rapidly when handover is required. Therefore, scanning is a key process of ensuring successful handover.
A scanning process in a prior art is shown in FIG. 1. Messages in the scanning process are an MOB_SCN_RSP message and an MOB_SCN_REQ message. The MOB_SCN_RSP message may be sent by the serving BS of an MS to the MS actively, or be sent by the serving BS of the MS to the MS after the serving BS of the MS receives an MOB_SCN_REQ message from the MS. The BS notifies the MS of the scanning start time, scanning type, and BS ID information of the BSs to be scanned by sending the MOB_SCN_RSP message to the MS.
Both the MOB_SCN_RSP message and the MOB_SCN_REQ message contain BS ID information. The BS sends the MOB_SCN_RSP message containing BS ID information to the MS to notify the MS of the BSs to be scanned. The MS sends the MOB_SCN_REQ message containing BS ID information to the serving BS to notify the serving BS of the BSs to be scanned. Therefore, the BS ID information in the MOB_SCN_REQ message determines objects that will be scanned by the MS, and the BS ID information in the MOB_SCN_RSP message determines the objects that will be scanned by the BS. Both the MOB_SCN_RSP message and the MOB_SCN_REQ message still contain scanning type information. Each BS ID in the MOB_SCN_RSP and MOB_SCN_REQ messages is mapped to one scanning type.
The BS ID information in the MOB_SCN_RSP and MOB_SCN_REQ messages may be divided into two parts. The following takes the MOB_SCN_REQ message as an example to describe the BS ID information. The BS ID information in the MOB_SCN_RSP message is similar to the BS ID information in the MOB_SCN_REQ message.
The MOB_SCN_REQ message is sent from the MS to the serving BS of the MS. The BS ID information contained in the MOB_SCN_REQ message is divided into two parts. The first part of BS ID information corresponds to the BS ID information contained in an MOB_NBR_ADV message of the serving BS, and the second part of BS ID information is the BS IDs corresponding to the BSs that will be actively scanned by the MS but not contained in the MOB_NBR_ADV message.
IEEE802.16e adopts BS indexes to represent the first part of BS ID information; that is, IEEE802.16e represents the first part of BS ID information by specifying the sequence of the BS IDs contained in the MOB_NBR_ADV message that the MS requests to scan. The specific method is to set a BS Index field in a scanning process message.
Generally, the number of the BS IDs contained in the MOB_NBR_ADV message cannot exceed 255. Therefore, the BS Index field is represented by only eight bits.
IEEE802.16e adopts full BS IDs to map the second part of BS ID information; that is, IEEE802.16e uses 48-bit BS IDs to specify the BSs that the MS requests to scan. The second part of BS ID information is mapped by adopting full BS IDs rather than BS indexes because the BSs corresponding to the second part of BS ID information will be actively scanned by the MS but the BS IDs of the BSs are not contained in the MOB_NBR_ADV message.
According to the foregoing descriptions, the format of an MOB_SCN_REQ message in a prior art is shown in FIG. 2.
The MOB_SCN_REQ message includes various fields, which are represented by numbers or letters in FIG. 2. The following describes these fields.
Field 1 is a Management Message Type field with a length of eight bits.
Field 2 is a Scan duration field with a length of eight bits.
Field 3 is an Interleaving interval field with a length of eight bits.
Field 4 is a Scan iteration field with a length of eight bits.
Field 5 is an N_Recommended_BS_Index field with a length of eight bits. The field indicates the number of the BS IDs corresponding to the BSs that will be scanned by an MS and contained in an MOB_NBR-ADV message.
Field 6 is a Configuration change count for MOB_NBR-ADV field in an MOB_NBR_ADV message with a length of eight bits.
Field 7 is a Neighbor_BS_Index field with a length of eight bits. The field indicates the sequence of the BS IDs corresponding to the BSs that will be scanned by an MS in an MOB_NBR-ADV message.
Field 8 is a reserved field with a length of one bit.
Field 9 is a Scanning type field with a length of three bits. The field indicates the scanning type of the BS ID information mapped to field 7. There are four scanning types, namely, scanning type 0, scanning type 1, scanning type 2, and scanning type 3.
Field 10 is an N_Recommended_BS_Full field with a length of eight bits. The field indicates the number of the BSs that will be actively scanned by an MS.
Field 11 is a Recommended BS ID field with a length of 48 bits. The field indicates the BS IDs of the BSs that will be actively scanned by an MS.
Field 12 is a reserved field with a length of one bit.
Field 13 is a Scanning type field with a length of three bits. The field indicates the scanning types of the BS IDs mapped to field 11.
When the value of field 5 is 0, fields 6-9 and field A are absent.
The contents of field A are “n” times of the contents of fields 7-9 in sequence and “n” is equal to the value of field 5.
The content of field B is a repetition of the contents of fields 11-13 in sequence and the number of repetitions is equal to the value of field 10.
Field C is another field in an MOB_SCN_REQ message.
In a prior art, the format of an MOB_SCN_RSP message is shown in FIG. 3. The representation method is the same as FIG. 2; that is, fields 1-14 represent 14 fields represented by numbers in ascending order starting from field 1 and fields 15-18 represent four fields represented by numbers in ascending order starting from field 15. The following describes the fields shown in FIG. 3.
Field 1 is a Management Message Type field with a length of eight bits.
Field 2 is a Scan duration field with a length of eight bits.
Field 3 is a Report mode field with a length of two bits.
Field 4 is a reserved field with a length of six bits.
Field 5 is a Report period field with a length of eight bits.
Field 6 is a Report metric field with a length of eight bits.
Field 7 is a Start frame field with a length of eight bits.
Field 8 is an Interleaving interval field with a length of eight bits.
Field 9 is a Scan iteration field with a length of eight bits.
Field 10 is an N_Recommended_BS_Index field with a length of eight bits. The field indicates the number of the BS IDs corresponding to the BSs that will be scanned by a BS and contained in an MOB_NBR-ADV message.
The contents and meanings of fields 11-14 are the same as the contents and meanings of fields 6-9 in FIG. 2 respectively. Field D between field 14 and field A is present when the scanning type of field 14 is scanning type 2 or scanning type 3. Field D is 24 bits in length.
In FIG. 3, the content of field A is a repetition of the contents of fields 12-14 and field D in sequence and the number of repetitions is equal to the value of field 11; field D is between field 14 and field A.
Field 15 is an N_Recommended_BS_Full field with a length of eight bits. The field indicates the number of the BS IDs corresponding to the BSs that will be scanned by a BS but not contained in an MOB_NBR-ADV message.
Field 16 is a Recommended BS ID field with a length of 48 bits. The field indicates the BS IDs corresponding to the BSs that will be scanned by a BS but not contained in an MOB_NBR-ADV message.
Field 17 is a reserved field with a length of one bit.
Field 18 is a Scanning type field with a length of three bits. The field indicates the scanning types of the BS IDs mapped to field 16.
Field D between field 18 and field B is present when the scanning type of field 18 is scanning type 2 or scanning type 3. Field D is 24 bits in length.
In FIG. 3, the content of field B is a repetition of the contents of fields 16-18 and field D in sequence and the number of repetitions is equal to the value of field 15; field D is between field 18 and field B.
Field E is another field in an MOB_SCN_RSP message.
According to the foregoing technical solution, one part of BS ID information in a scanning process message corresponds to the BS IDs contained in an MOB_NBR_ADV message, and therefore, a prior art adopts the BS Index mode to map this part of BS ID information and determines scanned objects according to the mapping. When the BS Index mode is adopted to map BS ID information, and thereby scanned objects are determined, each BS requires only eight bits. When the Full BS ID mode is adopted, each BS requires 48 bits. Therefore, when the BS Index mode is adopted to map the first part of BS ID information, and thereby scanned objects are determined, the air-interface resource usage is improved to a certain extent. Because the air-interface resources are rare resources, it is urgent to find a solution to further improvement of the air-interface resource usage in the wideband radio access system.